At present, the banks of spindles for short fibers, such as cotton fibers, are generally provided with an automatic removal of the bobbins, the automatic removal operation being relatively easy, while on banks of spindles for long fibers this operation is much more difficult to perform.
Thus, to be able to effect the removal of full bobbins, it is necessary to break the yarn and moreover this latter must be broken at the outlet of the blade of the presser finger. This operation is performed without difficulty in the presence of short fibers, such as cotton fibers, the carriage bearing the full bobbins being simply given a descending movement after the stopping of the bobbins and the flyers. This descending movement has as a result the breakage of the yarn on each bobbin at the outlet of the blade of the presser finger, as desired.
In the case of long fibers, this maneuver does not permit absolutely obtaining the same result. The yarn of long fibers breaks in the tube of the flyer and not at the outlet of the blade of the presser finger, which has the effect that all automation is rendered useless. The rethreading of the whole machine is necessary each time.
Thus, the yarns of long fibers, namely whose fibers have a mean length comprised between 5 cm and 20 cm, do not always break at the same place and generally have a weak point at a place where the yarn is stretched.
Moreover, as the winding operation generally ends at the upper portion of the bobbin, it is necessary to obtain a correct winding of the end of the broken yarn so as to permit the transportation of said bobbin without risk of unwinding.
Finally, it is also necessary, so as to be able to restart automatically a new winding cycle, that the broken end of the yarn, at the level of the presser finger, should be completely available.
In FR-A-2 665 188 there has been proposed stopping the machine at a distance near the lower reversal at the end of winding, then putting into operation again the winding members of the bank of spindles and simultaneously lowering the carriage beyond the wound material. A winding of several turns is then effected on the upper end of the bobbin, then the yarn supply is stopped while effecting an over-twisting of this latter for several turns. A yarn reserve is then delivered and the carriage is raised, which breaks the yarn before a new descent of the carriage into the doffing position for automatic removal of the full bobbins.
The solution proposed by this document certainly permits effecting breaking of the yarn while ensuring that the end of the latter will be entirely wound on the bobbin and that the automatic restarting of a new cycle will be possible, but because the broken end is available relatively high on the bobbin, it poses a problem for the operators for the retrieval of the yarn end remaining on the full bobbin, when the latter is suspended from a rack.